The bicarbonate-formate cycle has been described by Zaidman, Weiner and Sasson [Int. J. Hydrogen Energy, 11(5), pp. 341-347 (1986) and Weiner, Blum, Feilchenfeld, Sasson and Zalmanov [Journal of Catalysis, 110, pp. 184-190 (1988)], suggesting the use of aqueous formate solutions as hydrogen carriers. The bicarbonate-formate cycle consists of two stages, as shown by the following chemical equation:HCO3−+H2↔HCO2−+H2O
The first stage involves the reduction of bicarbonate to formate. To this end, a bicarbonate salt in aqueous solution is reacted with hydrogen at about 35° C. under hydrogen pressure, to give an aqueous solution of the corresponding formate salt. On demand, the reverse reaction is carried out, normally at about 70° and atmospheric pressure, whereby the formate is decomposed to produce the bicarbonate and hydrogen. The hydrogen can then be used for any desired purpose, e.g., as a fuel material. It follows that in the first stage (formate synthesis), the system is loaded with hydrogen, which is released and delivered in the second stage (formate decomposition). Both stages are carried out in the presence of a catalyst, e.g. heterogeneous catalyst such as palladium.
Kramer, Levy and Warshawsky [Int. J. Hydrogen Energy, 20(3), pp. 229-233 (1995)] investigated the activity of the catalysts used in bicarbonate-formate cycle, starting by reacting 3.5 M KHCO3 solution with hydrogen to give the formate. The authors reported that the activity of the palladium catalyst used decreases with time, demonstrating that the catalyst can be regenerated through the following sequence of steps: (i) separating the catalyst from the solution; (ii) washing with distilled water at ambient temperature; (iii) drying at 120° C. under argon atmosphere; (iv) oxidizing the catalyst with oxygen or air.
It would be beneficial to provide a process allowing enhanced hydrogen storage and production capacity, and on the same time, offering a convenient way for treating and regenerating the catalyst used.